We proposed to assess the risks and benefits of prolonged clopidogrel therapy (>12 months) versus <12 months among Veterans following percutaneous coronary interventions (PCI) with coronary stenting. Our primary aim is to assess the risk of death or myocardial infarction by type of coronary stent (bare-metal stents, 1st generation drug-eluting stents, and 2nd generation drug-eluting stents. We will use VA administrative and clinical databases to create two cohorts of patients receiving bare-metal and 1st generation drug-eluting stents between 2002-2007, and a second more contemporary cohort of patients receiving 2nd generation drug-eluting stents between 2008- 2010. Our data will be derived from the VA National Patient Care Database, which contains information on inpatient and outpatient details from the Patient Treatment Files (PTF) and Outpatient Clinic (OPC) files. Demographic data will be obtained from the VHA Vital Status file. Pharmacy data will be obtained from the Pharmacy Benefits Management system files, including medication prescriptions to estimate duration of therapy. In the 2008-2010 cohort we will also obtain data on procedural characteristics (e.g. stent length, diameter, number of stents, artery stented) as covariables from the VA Cardiovascular Assessment Reporting and Tracking (CART) database. For each stent type, we will use a landmark analysis strategy and Cox's proportional hazards regression to assess the risk of death or myocardial infarction in patients receiving prolonged clopidogrel > 12 months versus <12 months treatment. We will also evaluate the risk of prolonged clopidogrel therapy on the secondary endpoints of cardiac death, ischemic stroke, coronary revascularization with PCI or coronary artery bypass surgery, and major bleeding. As secondary aims, we will evaluate the interaction of prolonged clopidogrel and type of drug-eluting stent (1st or 2nd generation) by combining both cohorts. Using the same method, we will assess the risk of prolonged clopidogrel in subgroups of patients on chronic anticoagulation for other indications (e.g. atrial fibrillation). To evaluate potential data limitations we will perform chart reviews in a subsample of the cohorts to validate several key covariates, such as aspirin adherence. We will also evaluate the potential impact of confounding and confounding by indication by three methods: 1. Traditional multivariable adjustment, 2. Propensity score adjusted and matched analysis, 3. Restriction of the cohorts to patients with low risk characteristics. We will also conduct sensitivity analyses to assess the impact of missing covariate data. Exploratory analyses will evaluate the risks and benefits of more prolonged clopidogrel therapy beyond the landmarks of 18 months, 24 months and 36 months after PCI. The proposed research will provide valuable information to bridge the current information gap in the cardiology community regarding the risks and benefits of prolonged clopidogrel therapy in Veterans receiving coronary stents. These data may also inform future randomized trials to address the value of prolonged clopidogrel therapy.